package com.hackerrank.challenges.lonelyinteger;

import java.util.Scanner;

public class Solution {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int N = in.nextInt(), c[] = new int[101];
		for(int n = 0; n < N; n++)
			c[in.nextInt()]++;
		for(int i = 0; i < 101; i++)
			if(c[i] == 1)
				System.out.println(i);
	}
}
